Lecture 10 +11 Flashcards
Molluscs
What type of organism is a mollusc?
A lophotrochozoan that is a Protostomia with triploblast development and a larval form called trochophore.
What does “mollusca” mean, and how diverse is the phylum?
Mollusca” is Latin for “soft,” and it is an extremely diverse phylum with around 90,000 species across 8 classes.
Where can molluscs be found, and what are their feeding habits?
Molluscs have a cosmopolitan distribution (marine, freshwater, and terrestrial) and can be carnivores, herbivores, filter feeders, or parasites.
Why are molluscs important to humans?
They provide food (e.g., calamari, mussels), pearls, shells (used as currency like cowries), serve as bioindicators, pests, and have medical importance (e.g., shell strength, nerve cells).
What are the main body regions of molluscs?
Molluscs have a Head-Foot region and a Visceral Mass.
What is included in the Head-Foot region of molluscs?
he Head with sense organs (brain, eyespots, tentacles) and the Radula, a chitinous ribbon with teeth (absent in bivalves), and the Foot for locomotion, attachment, and mucus production.
What is the function of the radula?
The radula is a chain-saw-like structure that carries teeth on a chitinous ribbon, used for feeding (absent in bivalves).
What does the Foot region of a mollusc do?
The foot aids in locomotion, attachment, and can produce mucus for gliding.
What is the Visceral Mass in molluscs?
It contains the internal organs (digestive, excretory, reproductive, and respiratory) and is covered by the Mantle.
What is the mantle, and what does it do?
The mantle is the “skin” of the mollusc, often with muscles and chemoreceptors, and it secretes the shell.
Describe the mantle cavity in molluscs.
The mantle cavity is open to the environment, allowing water to flow around organs for excretion, respiration, and sometimes jet propulsion.
What are the three layers of the mollusc shell?
Periostracum: outer organic layer, resistant and thin with dark coloration.
Prismatic layer: middle layer, thick with calcium carbonate.
Nacre: inner layer, “mother of pearl,” continuously thickens.
How are pearls formed in molluscs?
When dirt enters between the shell and mantle, nacre is secreted around it, forming a pearl over time.
What are some basic internal characteristics of molluscs?
Bilaterally symmetric coelomates with reduced coeloms.
Most have an open circulatory system and a complex digestive system.
Describe the respiratory structures in molluscs.
Molluscs have a mantle cavity for respiration, which may include gills, lungs, or allow diffusion, open to the environment.
What are the different nervous system types in molluscs?
They range from simple (or non-existent) to complex brains and centralized nervous systems.
Describe the reproductive system in molluscs.
Mostly not asexual.
Can be dioecious (separate sexes) or monoecious (hermaphroditic).
Have trochophore larvae and commonly veliger larvae in aquatic forms
What are the two main clades in the old phylogeny of molluscs?
Aculifera and Conchifera.
What classes are included in the Aculifera clade?
Class Caudofoveata, Class Solenogastres, and Class Polyplacophora.
what are the classes in the Aplacophorans
Class Caudofoveata, Class Solenogastres
What are some characteristics of Class Caudofoveata and Solenogastres (spicule worms)
Wormlike, shell-less, with calcareous scales/spicules, reduced head, no foot, and are marine burrowers consuming detritus/microorganisms.
What defines Class Polyplacophora, also known as chitons?
They have 8 movable plates, a mantle girdle around the body, a central foot, multiple gills along the mantle cavity, and are intertidal grazers on hard surfaces.
What is unique about Class Monoplacophora?
Known as “one plate” molluscs with a single cap-like shell, serial repetition of soft parts, and are deep-sea grazers on hard surfaces.
Which class is the most diverse within the molluscs, and what organisms does it include?
Class Gastropoda, with around 70,000 species including snails, periwinkles, limpets, sea slugs, and slugs.
